Fan



Jan. 6, 1942. w, s ROBERTS 2,269,287

FAN

Filed NOV. 29, 1939' INVENTOR. WWI) 5f flap/f5 BY Wax/ ATTORNEY.

Patentedulan. 6, 1942 I UNITED. STATES PATENT azoam OFFICE 3Claims.

This invention relates to fans and particularly to the formation of. the blades thereof.

The primary object of the invention is to provide a blade formation which through rotation about an axis causes delivery of a compact,

-twisting column of air, of greater penetration than can be obtained by use of conventional fans of the same size and under like conditions.

Another object is to provide a fan blade formation such that the air set in motion thereby is drawn inwardly from the region adjacent the tip of the blade} rather than from the region directly back of the blade. In this respect the driving motor, shell or hull which is ordinarily located behind the fan does not act to obstruct or interfere with the intake of air to the fan, as is the case when the air is taken inwardly directly from the rear of the fan.

Another object is to reduce or nullify tip loss resulting from centrifugal slippage by causing, through a particular blade formation, a centripetal movement of air.

Another object is to provide a fan blade formation which is characterized by low resistance in entering static air, by low drag effect, and by the fact that air which moves inwardly to replace that air which has been displaced moves in the same general direction as the air first displaced, without requiring any abrupt change in direction of the air flow.

Another object is to provide a fan blade formation so designed that such undesirable characteristics as tip noise, blade flutter, cavitation, air-slap or "spanking are completely obviated or reduced to an extent that they become unnoticeable.

Other objects and advantages will become more fully apparent as reference is had to the accompanying drawing wherein my invention is illustrated, and in which:

Fig. 1 is a front elevation of the fan,

Fig. 2 is a side elevation,

Fig. 3 is a top plan, and

Figs. 4 to 11 are cross sections of a blade,

with the several sections being taken on planes indicated on Fig. 1 by lines bearing reference numerals which correspond, respectively, to the figure numbers.

More particularly. 20 designates the hub of a fan having three equally spaced blades 2| radiating, generally therefrom. The three blades are, of course, identical in all respects, and although three blades are shown, it will be understood that the novel blade characteristics hereinafter described might well be incorporated into a fan having another numberof blades. However, the blade characteristics hereinafter described produce a high degree of emciency when used in conjunction with a three-bladed fan,

Each blade is formed with its leading edge 22 curving in the direction of travel of the blade about the axisof the hub, and each blade has its tip portion 23 projecting or extending in the direction of travel and also curved or turned up in such manner that it projects or extends in the'direction of the axis of the hub, in the direction air is to be displaced. The trailing edge 24 is also curved in the direction of travel of the blade, giving the blade what might loose; ly be termed a crescent shape, or a quarter moon shape as viewed in front elevation.

As may be seen upon reference to Figs. 4 to 7., the radially outward portions of the blade are concavo-convex as viewedin cross section, with the concave surface of the blade constituting the front surface of the blade. Through the regions of the blade between the lines 1-1 and Ill-It the concave-convex shape gradually changes, becomes flattened, and becomes concave-convex again with the convex surface constituting the front surface of the blade.

and is rounded, as shown in Figs. 4 to 11, whereas the leading edge 22 is comparatively sharp. The blade section, in addition to the reversing concave-convex shape above described gradually tapers toward the sharp leading edge. This formation, particularly the sharp leading edge, is found to materially reduce the high frequency hissing noises which are found present when the edge is formed blunt.

Curvature of the blade in the direction of travel, and projection of the tip both in the direction of travel and forwardly in the direction of air movement, as above described, results in an air movement wherein the air moves inwardly centripetally over the face of the blade. That is to say, from the tip portion inwardly to approximately the region of the line air is drawn inwardly from the direction of the tip and is displaced spirally in front of the fan. As a result of this spiral movement of the air the air being displaced and that drawn in to replace it both move in the same general direction, without requiring an abrupt change in direction in the flow thereof.v

The above function wherein the air moves centripetally inwardly over the face of the blade is illustrated by the arrows II on Fig. 1. However, in the inner region of the blade, the concavo-convex portion wherein the convex surface is the front surface, the reverse action takes place, and the air moves centrifugally outwardly. The manner in which the air is drawn inwardly from the region outward with respect to-the blade tips is illustrated by the flow arrows 26 in Fig. 2.

Atlhough a specific embodiment of the invention is illustrated and described, it will be understood that various changes may be made within the scope of the appended claims without departing from the spirit of the invention, and such changes are contemplated.

What is claimed is:

1. A fan blade adapted to be rotated about an axis for displacing air, said blade having leading and trailing edges both curved in the direction of rotation of the blade, the curvature of the two edges being such that the widest portion of the blade is substantially mid-way between the inner end of the blade and the tip, the region of the bladeextending inwardly from the tip portion to at least the portion of greatest width, being of concave-convex cross section with the concave surface constituting the work face of the blade, the remainder of the blade changing to a concave-convex cross section with the convex surface constituting the work face of the blade.

2. A blade having an angle of attack and adapted to be rotated about an axis, said blade having a sharp leading edge and a blunt trailing edge and being gradually tapered from its portion of greatest thickness to the sharp leading edge, said leading and trailing edges both being curved in the direction of rotation with the curvature of the two edges correlated to form a shape such that the widest portion of the blade is substantially mid-way between-the inner end of the blade and the tip, the extreme tip portion or portion of greatest radius being curved and extended in the direction said axis extends, the portion of the blade extending from the tip portion to at least the widest portion of the blade being of concave-convex cross section with the concave surface constituting the front face of the blade, the remaining length of the blade changing progressively to a concave-convex cross section where the convex surface constitutes the front face of the blade.

3. A blade having an angle of attack and adapted to be rotated about an axis, said blade having a sharp leading edge and a blunt trailing edge and being gradually tapered from its .portion of greatest thickness to the sharp leading edge, said leading and trailing edges being curved in the direction of rotation with the curvature of the two edges correlated to form a portion of greatest width substantially mid-way between the tip and the inner end of the blade, the extreme tip portion or portion of greatest radius being curved and extended in the direction said axis extends in such manner as to 'set up a component of force toward the center and along the lateral surface of an imaginary cone, and also being curved and extended in the direction of rotation of the blade in such manner that the tip cuts the air first and prevents air from slipping along the leading edge to the tip, the portion of the blade extending from the tip portion a substantial portion of the length of the blade being of concave-convex cross section with the concave surface constituting the front face of the blade, the remaining length of the blade changing progressively to a concavo-convex cross section where the convex surface constitutes the front face of the blade.

WILMER S. ROBERTS. 

